We report inelastic light scattering measurements of lattice dynamics related to the incommensurate orbital order in CaMn7O12. Below the ordering temperature To≈250K, we observe extra phonon peaks as a result of Brillouin zone folding, as well as a soft vibrational mode with a power-law T-dependent energy, Ω =Ω0(1-T/To)1/2. This temperature dependence demonstrates the second-order nature of the transition at To, and it indicates that the soft mode can be regarded as the amplitude excitation of the composite order parameter. Our result strongly suggests that the lattice degrees of freedom are actively involved in the orbital-ordering mechanism.
Physical Review B
- Pub Date:
- September 2014
- Infrared and Raman spectra;
- Phonon-electron interactions;
- Condensed Matter - Strongly Correlated Electrons
- 7 pages, 8 figures